The present invention relates to a magnetic encoder apparatus to detect a rotation position of a rotating body.
Conventionally, a magnetic encoder apparatus to detect a rotation position of a rotating body is structured by, for example, as shown in FIG. 14, a magnetic drum 30 which is connected to a rotating body 10, and which has a recording medium 20 formed of magnetic coating or magnet material on its outer periphery, and a magnetic resistance element 40 which is opposed to the outer periphery through an air gap.
When an example of 4 bits is explained, the magnetic drum 30 is provided with a 4-track recording medium 20 arranged in the axial direction, and a signal of each bit (20, 21, 22, 23) is formed by being magnetized to N and S poles at a constant pitch for each track.
Two magnetic resistance elements 40 are arranged for each track, and its interval is xc2xd pitch of a bit signal. By waveform shaping each bit signal, as shown in FIG. 15, each bit signal is outputted as signals of 4 kinds of rectangular waveforms in which one rotation of the rotating body 10 is equally divided, and the absolute position is detected by their synthetic signal.
Further, a magnetic encoder apparatus in which a disk magnet is fixed on the rotating body, and N and S poles are magnetized in the one direction on the upper surface of the magnet, and one magnetic sensor is provided opposed to the magnet, and by detecting the variation of the magnetic field by the magnetic sensor, the rotation position of the rotating body on which the magnet is fixed is detected, is disclosed (for example, JP-A-62-237302)
Further, a magnetic encoder apparatus in which, in order to make the variation of the magnetic field to be sinusoidal wave-like, an undulation is provided on the outer periphery of the rotating body, and a magnetic recording medium is formed along the shape of the undulation, is disclosed (for example, JP-A-58-162813, and JP-A-63-243718).
However, in the conventional technology shown in FIG. 14, there are following problems:
(1) Because the tracks to record each bit are arranged in the axial direction, when the number of bits is increased, the length in the axial direction becomes long, therefore, the size reduction is difficult.
(2) When the number of tracks is increased, the magnetizing portions are increased, therefore, the processing man-hour is increased.
(3) Because magnetic resistance elements are provided corresponding to each track, when the number of bits is increased, the number of wiring is increased, and the assembling working becomes complicated and the working man-hour is increased, and the cost is increased.
Further, in the conventional technology shown in the JP-A-62-237302, there are following problems:
(1) Because the magnetic sensor is one, the absolute position of the rotating body can not be obtained.
(2) Because the magnetic sensor detects the magnetic flux near the border line of the magnetic poles, the linear portion of the output waveform can be used, however, the accuracy of the sinusoidal waveform is lowered, and the detection accuracy of one rotation is lowered.
Further, in the conventional technology shown in the JP-A-63-243718, the undulation by which the magnetic field is changed in the sinusoidal waveform, is provided on the outer periphery of the rotating body, however, in a micro rotation detector to detect the rotation of, for example, a micro motor, because the outer shape of the rotating body is very small, it is very difficult to exactly process the outer shape of the rotating body to a sinusoidal wave-like concave and convex or an ellipse, and the rotation detector having the high detection accuracy can not be obtained.
Accordingly, an object of the present invention is to provide a magnetic encoder apparatus in which the structure is simple, the accuracy is high, and cost is low and the size is small, and the absolute position is obtained.
In the present invention, in a magnetic encoder apparatus, which has: a permanent magnet fixed to the rotating body; a magnetic field detection element which is opposed to the permanent magnet through an air gap, and fixed to the fixed body; and a signal processing circuit to process a signal from the magnetic field detection element, the permanent magnet is formed disk-like, and is magnetized in one direction which is the direction perpendicular to a shaft of the rotating body, and the magnetic field detection element is arranged on the outer periphery side of the permanent magnet through an air gap.
Further, the fixed body is formed of a ring-like magnetic substance, and has an air gap in the peripheral direction, and the magnetic field detection element is provided in the air gap.
Further, for the magnetic field detection element, two pairs of 2 magnetic field detection elements, which are one pair, are provided at positions whose phases are shifted by 180xc2x0 from each other, wherein each pair of 2 magnetic field detection elements are formed such that their phases are different from each other by 90xc2x0 electric angles, and the signal processing circuit is provided with a differential amplifier to process a differential signal between magnetic field detection elements which are opposed to each other, and detects the absolute value of a position of the rotating body.
Further, the magnetic field detection element is formed such that a radial magnetic sensing portion to detect a radial magnetic field to the axis of the rotating body and a circumferential magnetic sensing portion to detect a circumferential magnetic field to the axis of the rotating body are proximately arranged, and at least one magnetic field detection element is provided.
Further, for the magnetic field detection element, the Hall effect element or the magnetic resistance element is used. Further, the permanent magnet is formed of any one of a ferrite magnet, Smxe2x80x94Co series magnet, Ndxe2x80x94Fexe2x80x94B series magnet, or distributed composite magnet in which each kind of the magnets are combined with each other by the high polymer material, and the linearly anisotropic magnet may also be used.
According to such the means, the structure becomes simple, and because the rate of sinusoidal wave of the output signal from the magnetic field detection element is greatly increased, thereby, the position of the rotating body can be accurately detected.